title: Motion-weighted target volume and dose-volume histogram: a practical approximation of four-dimensional planning and evaluation.
abstract: OBJECTIVE
  In ITV-based 3D-planning, the information of volume occupancy versus respiratory phase is not utilized. We propose a motion-weighted CTV (mwCTV) delineation method, which carries some 4D-information into planning. This method allows plan optimization based on occupancy-weighting and generation of motion-weighted DVH (mwDVH) that approximate the DVHs of full 4D-dose accumulation.
  
  
  METHODS
  Occupancy information from contours in 4D-CT is incorporated in the mwCTV generation. Higher-occupancy volumes receive higher dosimetric priority in planning. The temporally-weighted mwCTV is converted to a spatially-weighted mwCTV incorporating the temporal-weighting in mwDVH generation using the 3D-dose distribution. The mwDVHs were compared with DVHs of deformable-image-registration (DIR)-based 4D-dose accumulation and 3D-method for 10 cases.
  
  
  RESULTS
  For all the cases, the mwDVH curves are closer to the 4D-calculated DVH than the 3D-DVHs are, indicating a better approximation of the 4D-DVH. The 70 Gy-covered percentage-CTV volume differed by -2.8% ± 0.8% between 3D and 4D, and 0.3% ± 0.7% between mwDVH and 4D-methods. The mean RMS values of the percentage-volume differences for the 4D-3D is 1.7 ± 1.1, while for the 4D-mwDVH is 0.4 ± 0.3.
  
  
  CONCLUSIONS
  The mwCTV and mwDVH method, which is simple in implementation and does not require DIR, is a practical approximation of DIR-based 4D-planning and evaluation.
authors.affiliation: Division of Radiation Oncology, Moffitt Cancer Center, Tampa, FL 33612, USA.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Zhang
authors.forename: Vladimir
authors.initials: V
authors.lastname: Feygelman
authors.forename: Tzung-Chi
authors.initials: TC
authors.lastname: Huang
authors.forename: Craig
authors.initials: C
authors.lastname: Stevens
authors.forename: Weiqi
authors.initials: W
authors.lastname: Li
authors.forename: Thomas
authors.initials: T
authors.lastname: Dilling
mesh_terms: D006801:Humans; D021621:Imaging, Three-Dimensional; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009038:Motion; D015641:Radiography, Interventional; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods